Injection molding electrical control switching power supply

Switching power supplies play an important role in the control system of injection molding machines, are an important component, and are components that are more prone to failure. The switching power supply mainly includes an input power grid filter, an input rectification filter, a converter, an output rectification filter, a control circuit, and a protection circuit. Their function is:

1. Input grid filter: Eliminate interference from the power grid, such as motor start, electrical switch, lightning strike, etc., and also prevent high-frequency noise generated by the switching power supply from spreading to the power grid.

2. Input rectifier filter: rectify and filter the grid input voltage to provide DC voltage to the converter.

3. Converter: is a key part of the switching power supply. It converts the DC voltage into a high frequency AC voltage and acts to isolate the output from the input grid.

4. Output rectification filter: rectify and filter the high-frequency AC voltage output from the converter to obtain the required DC voltage, and also prevent high-frequency noise from interfering with the load.

5. Control circuit: Detects the output DC voltage and compares it with the reference voltage for amplification. The pulse width of the oscillator is modulated to control the converter to maintain the output voltage stable.

6. Protection circuit: When the switching power supply has an overvoltage or overcurrent short circuit, the protection circuit stops the switching power supply to protect the load and the power supply itself.

Some readers will have such a question, first turn the 220V AC into DC, then turn the DC into AC through the converter, and finally turn the AC into DC output, and take such a big circle, why not put 220V The alternating current directly becomes the required DC? In fact, the AC mains is firstly transformed by the power transformer, and the unsteady DC voltage is obtained after rectification and filtering, and then the required DC voltage is obtained after adjustment. This power supply technology is mature and can achieve high stability and ripple. Very small, and there is no interference and noise from the switching power supply. However, its shortcoming is that it requires a large and cumbersome power frequency converter. The required filter capacitor has a large volume and weight, and the adjustment tube is operated in a linear state. There is a certain voltage drop on the adjustment tube, and the output is large. When the operating current is applied, the power consumption of the adjusting tube is too large, the conversion efficiency is low, and a large heat sink is also installed. In short, this power supply is not suitable for computers.

Switching power supplies mainly have the following characteristics:

1. Small size and light weight: Since there is no power frequency transformer, the volume and weight are only 20-30% of the linear power supply.

2. Low power consumption and high efficiency: The power transistor works in the switching state, so the power consumption on the transistor is small, the conversion efficiency is high, generally 60 to 70%, and the linear power supply is only 30 to 40%.

Relay in injection molding electrical control

First, the working principle and characteristics of the relay

A relay is an electronic control device that has a control system (also called an input loop) and a controlled system (also called an output loop). It is usually used in an automatic control circuit. It actually uses a small current to control the larger An "automatic switch" of current. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.

1. Working principle and characteristics of electromagnetic relay

Electromagnetic relays are generally composed of a core, a coil, an armature, a contact spring, and the like. As long as a certain voltage is applied to both ends of the coil, a certain current flows in the coil, thereby generating an electromagnetic effect, and the armature will absorb the pulling force of the return spring against the iron core under the action of the electromagnetic force attraction, thereby driving the armature. The moving contact is in contact with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic suction force also disappears, and the armature returns to the original position at the reaction force of the spring, so that the movable contact is attracted to the original static contact (normally closed contact). This is sucked and released, thereby achieving the purpose of turning on and off in the circuit. For the "normally open, normally closed" contacts of the relay, it can be distinguished as follows: a static contact that is in an open state when the relay coil is not energized, called a "normally open contact"; a static contact that is in an on state It is a "normally closed contact".

2. Working principle and characteristics of thermal reed relay

The thermal reed relay is a new type of thermal switch that uses temperature sensitive magnetic materials to detect and control temperature. It consists of a temperature-sensitive magnetic ring, a constant magnetic ring, a reed switch, a thermally conductive mounting piece, a plastic substrate, and other accessories. The thermal reed relay does not use coil excitation, and the magnetic force generated by the constant magnetic ring drives the switching action. Whether the constant magnetic ring can supply the magnetic force to the reed switch is determined by the temperature control characteristics of the temperature sensitive magnetic ring.

3. Working principle and characteristics of solid state relay (SSR)

The solid state relay is a kind of four-terminal device with two terminals as the input terminals and the other two terminals as the output terminals. The isolation device is used to realize the electrical isolation of the input and output. Solid state relays can be classified into AC type and DC type according to the type of load power supply. According to the switch type, it can be divided into normally open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type and photoelectric isolation type, and the photoelectric isolation type is the most.

Second, the main technical parameters of the relay

1, rated working voltage

It refers to the voltage required by the coil when the relay is working normally. Depending on the type of relay, it can be either an AC voltage or a DC voltage.

2, DC resistance

Refers to the DC resistance of the coil in the relay, which can be measured by a universal meter.

3, pull-in current

It refers to the minimum current that the relay can generate the pull-in action. In normal use, the given current must be slightly larger than the pull-in current so that the relay can operate stably. For the working voltage applied to the coil, generally do not exceed 1.5 times the rated working voltage, otherwise a large current will be generated and the coil will be burnt.

4, release current

It is the maximum current that the relay generates to release. When the current in the state of the relay is reduced to a certain level, the relay will return to the unenergized release state. The current at this time is much smaller than the pull-in current.

5, contact switching voltage and current

Refers to the voltage and current that the relay is allowed to load. It determines the relay can control the voltage and current, and can not exceed this value when using, otherwise it will easily damage the contacts of the relay.

Third, the relay test

1, measuring contact resistance

Use the resistance file of the universal meter to measure the normally closed contact and the dynamic point resistance, the resistance value should be 0; and the resistance value of the normally open contact and the moving point is infinite. This makes it possible to distinguish between a normally closed contact and a normally open contact.

2, measuring coil resistance

The resistance value of the relay coil can be measured by the universal meter R×10 Ω file to judge whether the coil has an open circuit.

3. Measure the pull-in voltage and pull-in current

Find adjustable power supply and ammeter, input a set of voltage to the relay, and connect the current meter in the power supply circuit for monitoring. Slowly increase the power supply voltage and record the pull-in voltage and pull-in current when you hear the relay pick-up sound. For accuracy, you can try to average and try several times.

4, measuring the release voltage and release current

It is also connected test as described above. When the relay is pulled in, the power supply voltage is gradually reduced. When the relay is heard again, record the voltage and current at this time. You can also try several times to get the average release. Voltage and release current. Under normal circumstances, the release voltage of the relay is about 10 to 50% of the pull-in voltage. If the release voltage is too small (less than 1/10 of the pull-in voltage), it will not be used normally, which will threaten the stability of the circuit. The work is not reliable.

Fourth, the electrical symbol and contact form of the relay

The relay coil is indicated by a long square symbol in the circuit. If the relay has two coils, draw two long square boxes. At the same time, the relay symbol "J" is marked in the long box or next to the long box. There are two ways to represent the contacts of a relay: one is to draw them directly on the long square side, which is more intuitive. The other is to draw the respective contacts into their respective control circuits according to the needs of the circuit connection. Usually, the same text symbols are marked on the contacts and coils of the same relay, and the contact groups are numbered. To show the difference. There are three basic forms of relay contacts:

1. When the moving type (H type) coil is not energized, the two contacts are disconnected. After energization, the two contacts are closed. It is represented by the pinyin head "H" of the word.

2. When the breaking type (D type) coil is not energized, the two contacts are closed, and the two contacts are disconnected after energization. It is represented by the pinyin head "D" of the hyphenation.

3. Conversion type (Z type) This is the contact type. This contact group has three contacts, that is, the middle is a moving contact, and one of the upper and lower static contacts. When the coil is not energized, the movable contact and one of the static contacts are opened and the other is closed. After the coil is energized, the movable contact moves, so that the original disconnection is closed, and the original closed state is turned off, and the conversion is achieved. purpose. Such a set of contacts is called a changeover contact. It is represented by the pinyin head "z" of the word "turn".

Fifth, the choice of relay

1. First understand the necessary conditions

1 control circuit power supply voltage, the maximum current that can be provided;

2 voltage and current in the circuit being controlled;

3 The controlled circuit needs several sets and what forms of contacts. When a relay is selected, the power supply voltage of the general control circuit can be used as the basis for selection. The control circuit should be able to provide sufficient operating current to the relay, otherwise the relay pull-in is unstable.

2. After reviewing the relevant data to determine the conditions of use, you can find the relevant information and find out the model and specification number of the required relay. If there is a relay on hand, you can check whether it can be used according to the data. Finally consider whether the size is appropriate.

3. Pay attention to the volume of the appliance. If it is used for general electrical appliances, in addition to considering the chassis volume, small relays mainly consider the layout of the circuit board.

Note: The PET type embryo referred to here is formed by a reciprocating screw injection device and a hot runner mold.

Method for eliminating quality defects of two-step forming PET bottles

Internal quality defects of the embryo and its elimination method

The quality of the type of embryo is ultimately reflected in the blow molded product, for example, in stretch blow molding. Although effective measures are taken, the quality requirements of the bottle are still not met, which indicates that the internal quality of the parison is defective. In order to improve the internal quality of the embryo, the following points should be noted:

1) The material must be sufficiently dry and have a water content of less than 0.005%.

2) Keep the injection speed and plasticizing speed as low as possible, the plasticizing speed is 50-100r/min, and the screw line speed is 8m-15m/min.

3) Keep the plasticized back pressure as low as possible, with a back pressure of 0.5-1Mba.

4) The downtime of the resin in the barrel, hot runner body and hot runner nozzle is as short as possible.

5) The temperature of the hot runner body, hot runner nozzle and barrel is as low as possible.

6) The material drying temperature is as low as possible. ) The mold is cooled evenly

7) The holding pressure should not be too high, and the holding time should not be too long.

Third, the stretch blow molding PRT bottle is the last link of the molded PET bottle, which is directly related to the quality of the PET bottle. Therefore, the equipment involved in the stretch blow molding PET bottle must be strictly controlled to stretch blow molding. Produce high quality PET bottles.

*Manual semi-automatic blow molding PET bottle equipment

*Semi-automatic infrared rotation

Main function of the heater: using the infrared characteristics to uniformly heat the parison to the blow molding temperature

The heater is mainly composed of: an infrared lamp heating device with adjustable temperature, a central revolution mechanism for rotating the sprocket chain driven by a motor driven by a frequency conversion device, a rotation mechanism for inserting a parison on a public chain, a control cabinet And so on. Work cycle: Manual insertion of the parison, the embryo is revolved and rotated. Under infrared radiation, uniform heating is obtained, and the parison which reaches the blow molding temperature is manually taken out. * Stretch blow molding machine.

Main function: The preforms that reach the blow molding temperature are axially stretched and then blow molded with high pressure air.

Stretch blow molding machine mainly consists of: pneumatic mechanical clamping mechanism, pneumatic system, stretch blow molding device, mold, control system and so on.

Work cycle: The parison that reaches the blow molding temperature is manually placed in a single (double) side mold cavity, and the preform is self-aligned by its own bottle mouth thread, and then the mold is clamped and pressed. The sealing cylinder works, seals the bottle mouth, and stretches the cylinder to work. The stretching rod end is pressed against the bottom of the parison for axial stretching to the bottom of the cavity, and high-pressure air is blown into the inner cavity of the parison. After a certain period of pressure and cooling, the stretching rod is retracted, the sealing cylinder piston is retracted, the mold is opened, and the product (PET forming bottle) is taken out.

Defective methods for the quality of stretch blow molded PET bottles (see table below)

How to carry out precision injection molding

Most of the plastic electronic components are injection-molded. Since these plastic parts have high design precision and are processed by special engineering plastics, conventional injection molding cannot be used for these plastic parts, and precision injection molding technology must be adopted. In order to ensure the performance, quality and reliability of these precision plastic parts and the stability of long-term use, injection molding of plastic products with high quality and meeting product design requirements must be applied to plastic materials, injection molding equipment and mold design and injection molding, and injection molding. The site management is perfected.

We usually say that precision injection molding means that the precision of the molded product should meet strict dimensional tolerances, geometric tolerances and surface roughness. There are many relevant conditions for precision injection molding, and the most essential are the four basic factors of plastic materials, injection molds, injection molding processes and injection molding equipment. When designing plastic products, engineering plastic materials should be selected first, and engineering plastics capable of precision injection molding must use materials with high mechanical properties, dimensional stability, good creep resistance and environmental stress cracking resistance. Secondly, the appropriate injection molding machine should be selected according to the selected plastic material, the dimensional accuracy of the finished product, the weight of the part, the quality requirements and the expected mold structure. In the process of processing, the factors affecting precision injection molding products mainly come from the temperature of the mold, the control of the injection molding process, and the variation range of the ambient temperature and humidity at the production site and the annealing treatment of the acquired products.

For precision injection molding, mold is one of the keys to obtain precision plastic products that meet the quality requirements. The molds for precision injection molding should meet the requirements of product size, precision and shape. The mold materials should be strictly selected. However, even if the precision and size of the mold are the same, the actual size of the molded plastic article may be inconsistent due to the difference in the amount of shrinkage. Therefore, effective control of shrinkage of plastic products is very important in precision injection molding technology.

Whether the injection mold design is reasonable or not will directly affect the shrinkage rate of the plastic product. Since the mold cavity size is determined by the size of the plastic product plus the estimated shrinkage rate, the shrinkage rate is determined by the plastic manufacturer or the engineering plastics manual. A recommended range of values that are related not only to the gate form of the mold, to the location and distribution of the gate, but also to the crystal orientation (anisotropic) of the engineering plastic, the shape and size of the plastic product, and the distance to the gate. It is related to the location and is closely related to the mold cooling distribution system. The main factors affecting plastic shrinkage are heat shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery. These factors are related to the molding conditions or operating conditions of precision injection molded products. Therefore, the relationship between these influencing factors and injection molding conditions and their apparent factors must be considered when designing the mold, such as injection pressure and cavity pressure and filling speed, injection melt temperature and mold temperature, mold structure and gate form and distribution. And the influence of the cross-sectional area of the gate, the wall thickness of the product, the content of the reinforcing filler in the plastic material, the crystallinity and orientation of the plastic material. The influence of the above factors is also different due to different plastic materials, other molding conditions such as temperature, humidity, continued crystallization, internal stress after molding, and changes in the injection molding machine.

Because the injection molding process is the process of converting plastic from solid (powder or pellet) to liquid (melt) to solid (product). From the pellets to the melt, from the melt to the product, the temperature field, stress field, flow field and density field are used in the middle. Under the action of these fields, different plastics (thermosetting or thermoplastic, crystallinity) Or non-crystalline, reinforced or non-reinforced, etc.) have different polymer structural morphology and rheological properties. Any factors affecting the above field will affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products. Thus, the intrinsic link between process factors and polymer properties, structural morphology, and plastics is manifested by plastics. It is important to analyze these intrinsic links to rationally formulate injection molding processes, rationally design and manufacture molds according to drawings, and even select injection molding equipment. Precision injection molding and ordinary injection molding also differ in injection pressure and injection rate. Precision injection molding often uses high pressure or ultra high pressure injection and high speed injection to obtain a small molding shrinkage. In view of the above various reasons, in addition to considering the design elements of the general mold, the following points must be considered when designing the precision injection mold: 1 use appropriate mold dimensional tolerance; 2 prevent mold shrinkage error; 3 prevent injection molding deformation; 4 Prevent demoulding from occurring; 5 minimize mold manufacturing errors; 6 prevent mold accuracy errors; 7 maintain mold accuracy.

The shrinkage rate will change due to the injection pressure. Therefore, for a single cavity mold, the cavity pressure in the cavity should be as uniform as possible; as for the multi-cavity mold, the cavity pressure between the cavities should be small. In the case of single cavity multi-gate or multi-cavity multi-gate, it must be injected at the same injection pressure to make the cavity pressure uniform. To do this, you must ensure that the gates are balanced. In order to make the cavity pressure in the cavity uniform, it is preferable to keep the pressure at the gate entrance consistent. The equilibrium of the pressure at the gate is related to the flow resistance in the runner. Therefore, before the gate pressure reaches equilibrium, the flow should be balanced first.

Since the melt temperature and the mold temperature have an effect on the actual shrinkage rate, in order to facilitate the determination of the molding conditions, it is necessary to pay attention to the arrangement of the cavities when designing the precision injection mold cavity. Because the molten plastic brings heat into the mold, the temperature gradient of the mold generally surrounds the cavity, forming a concentric shape centered on the main channel.

Therefore, design measures such as flow channel equalization, cavity arrangement, and concentric circular arrangement centered on the main channel are necessary to reduce the shrinkage error between the cavities, to extend the allowable range of molding conditions, and to reduce costs. . The cavity arrangement of precision injection molds should meet the requirements of flow channel equalization and centering on the main channel, and must adopt the cavity arrangement with the main channel as the symmetry line. Otherwise, the shrinkage rate difference of each cavity will be caused. .

Since the mold temperature has a great influence on the molding shrinkage rate, and also directly affects the mechanical properties of the injection molded article, it also causes various molding defects such as fading on the surface of the product, so the touch tool must be kept within the specified temperature range, and The mold temperature does not change with time. The temperature difference between the cavities of the multi-cavity mold must also not change. For this reason, temperature control measures for heating or cooling the mold must be taken in the mold design, and in order to minimize the temperature difference between the mold cavities, the design of the temperature control-cooling circuit must be paid attention to. In the cavity and core temperature control loop, there are mainly two connection modes: series cooling and parallel cooling.

From the perspective of heat exchange efficiency, the flow of cooling water should be turbulent. However, in a parallel cooling circuit, the flow in one circuit that is split is smaller than the flow in the series cooling circuit, which may result in laminar flow, and the flow actually entering each circuit is not necessarily the same. Since the temperature of the cooling water entering each circuit is the same, the temperature of each cavity should be the same, but in fact, the flow rate in each circuit is different, and the cooling capacity of each circuit is also different, so that the temperature of each cavity is impossible. Consistent. The disadvantage of using a series cooling circuit is that the flow resistance of the cooling water is large, and the temperature of the cooling water at the entrance of the front cavity is significantly different from the temperature of the cooling water at the inlet of the last cavity. The temperature difference between the cooling water inlet and outlet varies depending on the flow rate. For small precision injection molds for processing plastic parts, it is generally preferable to use a series cooling circuit from the viewpoint of reducing the mold cost. If the performance of the mold temperature controller (machine) used can control the flow rate of the cooling water within 2 ° C, the temperature difference of each cavity can be maintained at a maximum of 2 ° C.

The mold cavity and core should have their own cooling water circuit system. In the design of the cooling circuit, the thermal resistance of the circuit structure is different due to the difference in heat taken from the cavity and the core, and the temperature of the water at the inlet of the cavity and the core generates a large temperature difference. If the same system is used, the design of the cooling circuit is also difficult. In general, small injection mold cores for plastic parts are very small, and it is difficult to use a cooling water system. If possible, cores made of bronze may be used, and for solid bronze cores, plug-in cooling may be used. In addition, when taking measures against warpage of the injection molded article, it is also desirable to maintain a certain temperature difference between the cavity and the core. Therefore, the temperature adjustment and control should be carried out separately when setting the cooling cavity of the juice cavity and the core. In order to maintain the accuracy of the mold under the injection pressure and clamping force, the feasibility of grinding, grinding and polishing the cavity parts must be considered when designing the mold structure. Although the processing of the cavity and the core has reached the requirement of high precision, and the shrinkage rate is the same as expected, due to the center deviation during molding, the relevant dimensions of the inside and the outside of the formed product are difficult to reach the plastic. Design requirements for components. In order to maintain the dimensional accuracy of the dynamic and fixed model cavity on the parting surface, in addition to the guide column and guide sleeve centering commonly used in conventional molds, it is necessary to add a positioning position such as a tapered positioning pin or a wedge block to ensure accurate positioning accuracy. ,reliable.

Precision injection molding technology is the main and key production technology of plastic parts, and the design of precision injection mold is the main part of this production technology. Reasonable design of precision injection mold is the basis and necessary prerequisite for obtaining precision products. By reasonably determining the size and tolerance of the mold, taking measures to prevent shrinkage of the injection molded product, injection molding deformation, demoulding deformation, overflow, etc., as well as technical measures such as ensuring mold precision, and adopting the correct precision injection molding process, applicable engineering plastics Materials and precision injection molding equipment to achieve the best match!